Polymers or copolymers of acrylic acid, crosslinked with polyfunctional vinyl monomers have been well-known since several decades. They are used as thickening, viscosizing, gelling, stabilizing agents of solutions, suspensions, emulsions. Their use is widespread in several industrials fields, such as for example inks, paper, textile printing, cleaning products, as well as in the food, cosmetic and pharmaceutical industry. There is a wide patent literature relating to the preparation and use of these polymers; for example in patent specifications U.S. Pat. No. 2,798,053, U.S. Pat. No. 2,980,655, U.S. Pat. No. 4,375,533, the preparation thereof is disclosed, while specific uses are disclosed for example in patent specifications EP 0 323 209, EP 0 268 164, DE 1 904 309, EP 0 210 130.
These polymers, which generally are in the form of very fine and light powders, are marketed in acid form. Their practical use indeed presents some difficulties. In fact, polymers in the acid form must be dispersed before in order to obtain a homogeneous and optimal dispersion; to this end suitable stirring systems are necessary, special addition methods of the powdery product to the dispersing fluid and long stirring times are required.
Further, the subsequent neutralization with bases can imply some practical difficulties, since the diffusion of the neutralizing agent into the polymer is not immediate, thus unwanted gels and lumps, which are difficult to dissolve, are likely to form.
Patent specification U.S. Pat. No. 5,256,737 discloses the preparation and the use of salts of polymers in the form of powder. These already salified polymers overcome the drawbacks raised by the preparation of the acid predispersions and their subsequent neutralization, but the drawbacks of the laborious method of addition to avoid the formation of lumps, the cumbersome handling of a very light powder, which is very difficult to handle with automatic dosage equipments still remain.
Patent specification IT 1,201,130 discloses dispersions of crosslinked polymers or copolymers of acrylic acid in C.sub.7 -C.sub.22 fatty acids. By the use of these dispersions the handling of powders is avoided, but not the drawbacks from the use of polymers in the acid form, namely rather long stirring times necessary for the preparation of the aqueous dispersions, even because the dispersing phase is hydrophobic, and their subsequent neutralization.
Patent specification FR 2,677,655 discloses a process for the preparation of dispersions of crosslinked acrylic polymers or copolymers, in already salified form wherein the dispersing phase consists of C.sub.7 -C.sub.22 saturated or unsaturated fatty acids. According to this process, a salt of the previously prepared polymer is added, or the salified polymer is "instantly prepared" by adding the acrylic polymer to a methanolic solution of an alkali metal. The methanolic suspension of the resulting salt is admixed with a fatty acid or with a mixture of fatty acids and subsequently the methanol is distilled off, which shall be purified before its recycle, if any.
Both preparation methods of these dispersions are rather laborious and costly.
Patent specification EP 0 383 057 discloses the preparation of salts of crosslinked acrylic polymers directly by emulsion polymerization of the monomers in the form of salts and subsequent removal of water by azeotropic distillation. In this case the dispersing phase consists of a mineral oil.
In the above disclosed processes, other than the difficult preparation, dispersions of salified polymers are obtained in hydrophobic solvents. In many cases these dispersions are not useful, particularly in the cosmetic and detergent field, when gels, lotions or other formulates, whose main characteristic is limpidity, are to be prepared.
As far as the textile printing field is concerned, more or less fluid dispersions of salified polymers, wherein the dispersing phase consists of a water-hydrocarbon mixture, are marketed. These formulates, of special use in printing pastes, have been marketed since a long time. They are prepared according to well-known processes from the powdery polymers or directly by emulsion polymerization as disclosed for example in patent specification DE 3,641,700.
But these formulates, due to their high mineral oil content, pollute the environment (air, earth, water), therefore, for ecological reasons, their use is more and more restrained and a next to the future ban can be expected.
Accordingly, there is an urgent technological need of new products, which are able to obviate all the above mentioned difficulties or drawbacks and which are ready to the use, of easy and simple use and which do not pollute the environment.